have an array as a cookie value

hi every one i am having a php code and as you see i get id in it from another page. i want to save this id's in array based on cookies i did that too but i have a problem with it when i set timeout for example to 20 seconds and refresh page every 20 second it works fine but when i refresh it under 20 seconds it gives me this error i do not know why could u please help i am stuck with it like 2 hours thank u